Luminous Landscape Forum
Raw & Post Processing, Printing => Colour Management => Topic started by: torger on May 27, 2015, 03:17:59 pm
-
I just bought two MR-16 35W Solux halogen black back, 4700K.
According to the data sheet it should provide 4700K in the central bright circle at 12V. Both my lamps provide about ~3900K, and I need to step up to 16 volts to get ~4600K. This is a bit of a disappointment as the idea was reaching 5000K on mild overdrive, and my variable dc power supply can't output more than 16 volts.
So I'm wondering if the marking is exaggerated? Maybe these new black back lamps (before they just let red light out the back) has lowered the color temperature of the lamps?
Surfing the net I get mixed messages if they can do 4700K or not, but it seems many have had problems measuring the lower temperature outer disc or the light going out the back, but I'm just measuring the central disc.
I've attached spectral plots for 12 and 16 volts. From the shape of the spectra I think looks like it's losing power too fast from 550 and down, not enough blue is coming out.
Comparing to the spectral curve Solux presents themselves it doesn't match: http://www.solux.net/ies_files/SoLux%20Spectral%20Data.xls.pdf
The difference between 450 and 600 nm in my 12 volt spectra is 2x and only 1.46x in Solux data.
EDIT June 15: the problem was shown to be an issue with my cables(!), the lamps are fine. What seemed to be 16 volts over the lamp was much less. To drive the Solux lamps in overdrive make sure you have a power source that can deliver not just the volts, but also the amperes required, and make sure that the lab cables (often design for low power) can handle that without power loss.
-
So I'm wondering if the marking is exaggerated?
Maybe, what you report I've also seen as well. Do a search, it's been discussed here a number of times. Here's a screen capture of what I saw and it was shown in the posts on here:
http://forum.luminous-landscape.com/index.php?topic=79604.0
(http://digitaldog.net/files/Solux4700K.jpg)
-
Wow... that was a heated debate in that thread... surfing the net it seems like everything around solux is kind of controversial, I wonder why, it's just a lamp.
I just want to get a D50 simulator for some camera profiling testing, but so far this does not cut it.
-
Wow... that was a heated debate in that thread... surfing the net it seems like everything around solux is kind of controversial, I wonder why, it's just a lamp.
I just want to get a D50 simulator for some camera profiling testing, but so far this does not cut it.
Yes, heated. I think most of us are using Solux due to their spectrum and light qualities and as I think I mentioned, the numbers vary depending on the device used and calculated and I personally don't really care about the numbers. For your needs, I don't know of a better man made illuminate but if you need to hit specific numbers, you may have to try some different Solux lamp options.
-
According to the data sheet it should provide 4700K in the central bright circle at 12V. Both my lamps provide about ~3900K, and I need to step up to 16 volts to get ~4600K.
Almost sounds like they have been mis-labelled.
Note that lamp life is aprox. proportional to Voltage ^ -12. So a 1% increase in voltage reduces life to 90% of normal, while 16 Volts would be expected to reduce the life of a 12V lamp to 3% of normal.
-
Almost sounds like they have been mis-labelled.
Note that lamp life is aprox. proportional to Voltage ^ -12. So a 1% increase in voltage reduces life to 90% of normal, while 16 Volts would be expected to reduce the life of a 12V lamp to 3% of normal.
Thanks, I'll contact the seller. Yes I'm aware of that I'm burning the lamps fast, but for camera profiling they won't run for long, and I bought two not to light with two lamps (I use flatfield correction to even out uneven light) but to have one extra when one burns out :-).
16 volts was way higher than expected though, according to the overdrive data sheet it's considerably lower voltage required to reach 5000K, but that assumes the lamp starts at 4700K at 12V, not 3900K :-\
Looking at the data sheet of how the spectral shapes for the lower temperature should look it doesn't seem like it is a regular mislabelling, and the lamps reflector looks really blue and it's black back. The spectrum shape seems to match the 4700K lamp data from 500nm and up (it's almost flat at 12 volt, as it should be), red is rolled off the way it should, but it doesn't output enough blue.
My guess is that they have manufacturing issues, some series are good (I doubt they have made up their measurement data), but some are bad and doesn't meet specs. Or this whole black back series is bad, AFAIK all measurements I've seen that meet 4700K is done on the older unpainted model.
The best man-made illuminant currently commercially available to simulate real light is as far as I know Image Engineering's programmable multi-channel LED (http://image-engineering-shop.de/shop/article_iQ-LED/IQ-LED.html), I would be all over it if it cost 400 euro, but it's 6000... way outside my budget. Solux is super-cheap, now if it just worked as promised.
-
If someone happens to surf to this thread, adding this link for reference:
http://www.liulabs.com/Daylight.htm
A filtered halogen lamp that depending on configuration can do D50, D55, D65 and D75. It's $300 though so it's not for everyone.
Haven't decided yet, but I might go down this path, it would be nice with a proper D65 simulator for my camera profiling software development.
-
This is not my experience. I use a regulated power supply with dc out. I regulate it such that I have 12volts on the bulb terminals. I get 4600 - 4700 kelvin .
i use two to illuminate my prints and one has a Lee blue filter. Together it gives 5100 kelvin.
-
I get 4600 - 4700 kelvin .
What instrument and software are you using?
-
What instrument and software are you using?
may be there is also a difference between batches - say they used to be better and now Solux decided to cut some corners, no ?
-
may be there is also a difference between batches - say they used to be better and now Solux decided to cut some corners, no ?
I've talked to my dealer that sold me the lamps, he tested one from the same batch with a i1Pro and got 4600K I think it was, ie on spec (4700K +/-200K or so). I don't think I've done any mistake in measurement, but I'm getting kind of paranoid.
When you ask why you get a lower temperature than the spec you get this long list of all the mistakes they think you have made. The only thing I have left on that list is that my instrument would be faulty. Unfortunately I have not managed to get my paws on a second instrument to doublecheck. Other lamps measure as expected though, so I have no reason to suspect that it's faulty.
So my best theory is that there is some huge sample-to-sample variation going on. I'll probably ask the dealer to send me the lamp he tested, but I've kind of lost the apetite for Solux, and I what I really want is D65, not D50.
-
What instrument and software are you using?
One thing is that undiffused Solux bulbs are directional. This affects measurements if you aren't aware of this. I just measured (using ArgyllPro ColorMeter with a ColorMunki) a 36 degree 4700K Solux bulb that was mounted in a home made fixture, pointing down at my copy stand base.
(http://gallery.frogymandias.org/display/2015-06-05_ll-1/0001_img_4304_std.jpg)
When I put the ColorMunki in the center of the beam I got
(http://gallery.frogymandias.org/display/2015-06-05_ll-1/0002_img_4299_std.jpg)
(http://gallery.frogymandias.org/display/2015-06-05_ll-1/0003_screenshot_2015-06-05-15-08-10_std.jpg)
4458K. When I moved the ColorMunki so it was outside the beam's spread I got
(http://gallery.frogymandias.org/display/2015-06-05_ll-1/0004_img_4300_std.jpg)
(http://gallery.frogymandias.org/display/2015-06-05_ll-1/0005_screenshot_2015-06-05-15-08-41_std.jpg)
3820K. When I moved the ColorMunki farther from the beam's center I got
(http://gallery.frogymandias.org/display/2015-06-05_ll-1/0006_img_4301_std.jpg)
(http://gallery.frogymandias.org/display/2015-06-05_ll-1/0007_screenshot_2015-06-05-15-09-16_std.jpg)
3334K. I tried this several times and it was repeatable (Well, as repeatable as would be expected with an ad hoc measuring system.)
I've been measuring CFLs and LEDs and they don't act like this. When the ColorMunki is off axis, the spectrum and color temp. don't change appreciably.
Wayne
p.s., I love ArgyllPro ColorMeter
-
I've measured in the same way, using a Colormunki. I have two lamps, one is 3900K, the other 4100K. Undiffused. It's very obvious that the highest temperature is had in the center, one sees that it projects a yellow disc outside the whiter center.
4450K like you get is also a bit on the low side, but I guess acceptable. The +/-200K stated together with these type of lamps should rather be stated up to 4700K, possibly 200-300 less. That they output higher temps seems to be extremely rare.
-
It's very obvious that the highest temperature is had in the center, one sees that it projects a yellow disc outside the whiter center.
Yeah, it is obvious, but Andrew asked about measuring techniques. Apparently the issue of how to measure a Solux bulb has been contentious in the past. I wanted to get the ball rolling by showing how I measured.
So we could at least resolve how to measure a Solux bulb: show your measuring technique like I did.
Wayne
-
It was not meant as criticism, just for other readers to understand. If one reads about Solux and has never seen one it seems like it's super-difficult to measure it, but really it should not be that difficult. So I do think there is a real problem with these lamps, that there are sample variations which is considerably larger than the official tolerance. I don't think everyone that has reported low temperatures have measured wrong.
1) don't use diffuser or a shade that may add reflections and alter the temp
2) measure in the center of the projected disk
3) make sure there's not a lot of other light bouncing around in the room that can disturb the measurement
4) ideally feed it with a variable DC power supply so you can check voltage
I'm still waiting to get my dealers tested sample, will probably get it next week.
-
Yeah, it is obvious, but Andrew asked about measuring techniques. Apparently the issue of how to measure a Solux bulb has been contentious in the past.
I think that's certainly a good possibility, that's why I asked. I wasn't at all anal about how I measured my Task Lamp (which has a diffuser too). I got a value that didn't jive with what it 'should be' but I've said from day one, I don't really care and would expect differing instruments and software to provide differing values too. I used an i1Pro-2, not a ColorMunki, I used BableColor, the method was admittedly sloppy compared to Wayne's. In the end, I don't know we can come to a good conclusion about differences in values reported from single samples of lamps and differing techniques of measuring and I wonder if it matters.
-
What instrument and software are you using?
i1pro2 and i1 display pro. I used i1profiler and also a french measuremet program. The programs gave a difference of 100 kelvin .
-
It matters if you're going to use it as a D50 simulator. If you don't need UV output a working Solux on slight overdrive is both the best and the cheapest one can get in that regard.
For typical viewing applications, probably less so, but those that bothered getting a 4700K lamp instead of a $4 standard 3200K lamp is probably not thrilled if it shows 3900K like one of mine...
-
The solux are directional for sure. I measure the central part. I played with diffuser but that significantly lowered the temperature.
I would love to have a lighting setup that has a broeder area of illumination.
-
It matters if you're going to use it as a D50 simulator.
The one light source that can really do that is 93 million miles away, and measuring the CCT value of a man made illuminant with varying instruments and software isn't isn't going to convince me that Solux can do so.
-
Outdoor sunlight is varying heavily over the day, weather, location and time of year. Here up north we have months in a row when experiencing something similar to D50 is just a distant dream :).
If your experiments needs a fixed reference for repeatability D50 is there, a standardized average type of daylight. Color science is built around standardized light sources, using simulators more often than real daylight. Without simulators it would be very difficult to make scientific work as it requires repeatability and agreed standards. In the textile and print industry using a fixed repeatable reference which clients agree on is also important, making simulators more suitable than real daylight.
A simulator must replicate the important properties of daylight. Halogen-based simulators lack the spikes you find in fluorescent simulators which can be important in some applications, camera profiling is one. In other applications UV-content is more important (making effect of OBA visible for example) and then fluorescent simulators can be better, although adding a specific UV light source beside your halogen simulator can be even better.
LED is the future in daylight simulators though, high end reference viewing stations from Just Normlicht for example has already LEDs, but they're still extremely expensive. A low cost alternative are UV-pumped white LEDs which look promising (Yuji seems to be the leading company on that tech), I'm not sure they can rival filtered halogens though.
According to data I've seen a voltage-tuned Solux 4700K seems to be performing just as good as a $5000 multichannel LED when it comes to simulating D50. Next step up is stacked daylight filtered halogens, which is $300, probably only mariginally better.
-
No disagreement about what you've written torger in terms of Solux bulbs. I'm suggesting that this bulb is the best man made product I've used and at an affordable price and the there isn't a problem with them whether they reach CTT 4700K or not as the topic title suggests. Again, what multiple people using multiple products and bulbs report in terms of CTT doesn't matter. The plots of it's SPD are far more useful IMHO. As to how well they simulate D50, they key is deciding what one means by simulate and by how far from the goal of an average of real daylight measurements and using a CTT value as reported doesn't tell us that.
-
According to data I've seen a voltage-tuned Solux 4700K seems to be performing just as good as a $5000 multichannel LED when it comes to simulating D50.
but what about the very uneven illumination from Solux - it seems that if you are experimenting with it than you shall have a very hard time to fit the target within the area where you have consistent parameters...
-
In regards to hair splitting accuracy of simulated D50 artificial lighting has there been a study measuring the eye's adaptive nature compared to how a sprectro defines color differences in Delta E's?
Years back I found an Eizo pdf sales doc displaying a simple chart demonstrating the level of change between a Delta E 1 vs 2 vs 3 etc. showing the rate of change in what appeared to be a stock photo of Egypt's Sphinx. Delta E 3 I believe showed a marked change from 1 & 2.
Given that additional human influenced variable along with the rest Andrew and torger put forth I'm not seeing this level of accuracy helping photographers, but do kind of see it as necessary for programmers in helping them establish some type of standard for defining color mathematically under a simulated D50 artificial light for writing profiling software algorithms.
-
In regards to hair splitting accuracy of simulated D50 artificial lighting has there been a study measuring the eye's adaptive nature compared to how a sprectro defines color differences in Delta E's?
I assume that the CMC has published some papers (https://scholar.google.nl/scholar?q=Color+Measurement+Committee&hl=en&as_sdt=0&as_vis=1&oi=scholart&sa=X&ei=BYl0VZXmNImesAGiyID4Bw&ved=0CB8QgQMwAA) on the subject of Delta E (http://www.brucelindbloom.com/index.html?Eqn_DeltaE_CMC.html). In principle a delta E of 1 is supposed to be just noticeable. There are several other measurements of Delta E, like Delta E (CIE 1976) (http://www.brucelindbloom.com/index.html?Eqn_DeltaE_CMC.html), or Delta E (CIE 1994) (http://www.brucelindbloom.com/index.html?Eqn_DeltaE_CMC.html), or Delta E (CIE 2000) (http://www.brucelindbloom.com/index.html?Eqn_DeltaE_CMC.html).
Given that additional human influenced variable along with the rest Andrew and torger put forth I'm not seeing this level of accuracy helping photographers, but do kind of see it as necessary for programmers in helping them establish some type of standard for defining color mathematically under a simulated D50 artificial light for writing profiling software algorithms.
Indeed, it is inevitable for programming and research. There are too many human observer differences to pick one and promote it as a standard.
Cheers,
Bart
-
A deltaE of less than 1 between two color values is supposed to be imperceptible but to complicate matters, as Bart points out, there are several formulas for calculating this metric. Further the ability of the eye to distinguish two colors as different and is more limited for yellows but is better for greens and blues.
-
I assume that the CMC has published some papers (https://scholar.google.nl/scholar?q=Color+Measurement+Committee&hl=en&as_sdt=0&as_vis=1&oi=scholart&sa=X&ei=BYl0VZXmNImesAGiyID4Bw&ved=0CB8QgQMwAA) on the subject of Delta E (http://www.brucelindbloom.com/index.html?Eqn_DeltaE_CMC.html). In principle a delta E of 1 is supposed to be just noticeable. There are several other measurements of Delta E, like Delta E (CIE 1976) (http://www.brucelindbloom.com/index.html?Eqn_DeltaE_CMC.html), or Delta E (CIE 1994) (http://www.brucelindbloom.com/index.html?Eqn_DeltaE_CMC.html), or Delta E (CIE 2000) (http://www.brucelindbloom.com/index.html?Eqn_DeltaE_CMC.html).
Indeed, it is inevitable for programming and research. There are too many human observer differences to pick one and promote it as a standard.
Cheers,
Bart
Knowledgeable finds, Bart, but I was hoping to seeing the rate of change in the form of a visual sample and then show the adaptive change most humans see out in nature.
I often test my own eye's adaptive nature looking at the warm color of asphalt pavement lit by the open sun and then switch to checking the hue of a pecan tree bark in shade which is close to neutral and then look up at a blue sky that has a noticeable magenta tinge and look back at the tree bark and notice it looks more green.
What Delta E is that? Landscape photographers might depend on it when trying to remember what they saw out in nature during post processing.
-
What Delta E is that?
dE is derived by measurements. Of two solid samples. So the question can't be answered because the process you 'tested' doesn't fall into colorimetry but rather your subjective perception. As such we could both conduct your test, even side by side at the same time and come up with quite different conclusions.
-
dE is derived by measurements. Of two solid samples. So the question can't be answered because the process you 'tested' doesn't fall into colorimetry but rather your subjective perception. As such we could both conduct your test, even side by side at the same time and come up with quite different conclusions.
It's not my own subjective perception I can assure you. It happens viewing prints under a static artificial print viewing light after staring for an extended period of time at an open window during the day and looking back at both my display and prints. I shut my eyes for a while and the hue of both print and display returns back to the way they were during editing. Scenes captured and viewed on my display induce similar adaptive effects especially with greens lit by sunset.
It's a natural optical effect every human being lives with. I should know. I used to paint photorealistic renderings on illustration board and canvas. I'ld spend entire summers just looking at how daylight renders colors and noticing the differences between the mixed lighting of direct sunlight vs outdoor shade. It's not my objective perception. It's a real human condition and many don't bother to notice this when shooting outdoors.
But all this is just as an example of the many variables involved with how to define color perception mathematically to some standard. Maybe everyone's rate of change influenced by this adaptive effect is different between each individual but it still remains a real phenomenon and not some subjective judgement call on color perception.
-
It's not my own subjective perception I can assure you.
Of course it is. That's how our color vision works Tim.
It's a natural optical effect every human being lives with.
Yes but that's not something we can measure and produce a dE report. How would someone in her 20's differ from a male in his 60's and someone who suffers some degree of color blindness or has cataracts or had a couple glasses of wine or a few bong loads perceive this?
-
Of course it is. That's how our color vision works Tim. Yes but that's not something we can measure and produce a dE report. How would someone in her 20's differ from a male in his 60's and someone who suffers some degree of color blindness or has cataracts or had a couple glasses of wine or a few bong loads perceive this?
My comment and point is in reference to torger's requirements for exact Kelvin measurements from a D50 simulated artificial light (Solux) in order to attain a more accurate to scene editing starting point derived from a camera profile he's writing software for whose color target is lit by said D50 simulator.
Considering editing involves human visual intervention that exhibits adaptive visual behavior as I've described, makes this "accurate" starting point even more subjective since we humans don't rely on Delta E numbers measured from a spectro that records color with a static non-adaptive behavior. IOW what's accurate for one viewer may not be so for others.
But what I described about how I my eyes adapt viewing a landscape is real for me and I've seen this with others especially those asking for a by the numbers system for judging proper saturation levels editing images since their eyes take longer to adapt to newer edits.
-
But what I described about how I my eyes adapt viewing a landscape is real for me and I've seen this with others especially those asking for a by the numbers system for judging proper saturation levels editing images since their eyes take longer to adapt to newer edits.
I never said it wasn't real. I said it can't be described using dE which you asked about. Because apparently you don't yet understand, despite my posts, what you describe has nothing to do with dE or colorimetry.
-
I never said it wasn't real. I said it can't be described using dE which you asked about. Because apparently you don't yet understand, despite my posts, what you describe has nothing to do with dE or colorimetry.
dE from what I've understood it to be is the measure of color difference from a known and measured target. The rate of difference as it appears to a human has not been clearly defined. It would be helpful if photographers knew or had some kind of idea whether differences in dE as measured from a spectro is something to be concerned on how much it affects their editing and if having a more "accurate" to scene starting point is beneficial.
It doesn't appear that it's all that important in measuring dE differences caused by Kelvin number variations measured from a Solux light. But also it has not been shown how it affects the results derived from software driven camera profiles whose algorithms have these Solux induced Kelvin variations encoded in the creation of the camera profile.
-
dE from what I've understood it to be is the measure of color difference from a known and measured target.
No, it's the measure of difference between two solid colors. Take a pile of two sets of such readings, you can produce an average dE report. But that doesn't change the fact that the metric isn't based on anything you've described you perceive you've seen!
It would be helpful if photographers knew or had some kind of idea whether differences in dE as measured from a spectro is something to be concerned on how much it affects their editing and if having a more "accurate" to scene starting point is beneficial.
If they are concerned between the differences of two solid color samples, measured with a fixed illuminant in a Spectrophotometer, that's doable and easy. Again, it has no relationship to what you've described:
I often test my own eye's adaptive nature looking at the warm color of asphalt pavement lit by the open sun and then switch to checking the hue of a pecan tree bark in shade which is close to neutral and then look up at a blue sky that has a noticeable magenta tinge and look back at the tree bark and notice it looks more green.
What Delta E is that?
You're making a statement of what you visually perceive and then ask what the differences are based on the differences of two solid colors. You can't get an answer in dE!
It is like saying you intend to drive from California to Arizona and then asking what is the weight of the two states you hope to visit? The two have nothing to do with each other and further, how do you expect someone to answer the question about the weight?
It doesn't appear that it's all that important in measuring dE differences caused by Kelvin number variations measured from a Solux light.
The K numbers express a range of colors and we're not measuring two samples so the statement you've made doesn't make sense. Sorry. Two different software products, hooked up to the same instrument measuring the same Solux could very likely produce two different CCT values. Now what?
-
Exactly.
-
No, it's the measure of difference between two solid colors. Take a pile of two sets of such readings, you can produce an average dE report. But that doesn't change the fact that the metric isn't based on anything you've described you perceive you've seen!
but ultimately that is based on experiments on human sight... now the mere fact that those experients are far (timewise) removed from today and luckily (or not ?) were not conducted by Tim Lookingbill still does not change the fact about the origins of CIE color spaces, no ? ;)
-
but ultimately that is based on experiments on human sight... now the mere fact that those experients are far (timewise) removed from today and luckily (or not ?) were not conducted by Tim Lookingbill still does not change the fact about the origins of CIE color spaces, no ? ;)
Indeed, it IS based on experiments of human vision. OF TWO SOLID color samples in very ridged and controlled environments. What Tim is asking about his far, far more than two samples in such a condition, no?
-
Indeed, it IS based on experiments of human vision. OF TWO SOLID color samples.
popular sources saying a mixure of 3 illuminants
-
popular sources saying a mixure of 3 illuminants
Ah OK, but what's this have to do with Tim's request for a dE value based on: I test my own eye's adaptive nature looking at the warm color of asphalt pavement lit by the open sun and then switch to checking the hue of a pecan tree bark in shade. What Delta E is that?
-
Ah OK, but what's this have to do with Tim's request for a dE value based on: I test my own eye's adaptive nature looking at the warm color of asphalt pavement lit by the open sun and then switch to checking the hue of a pecan tree bark in shade. What Delta E is that?
I can only say that it was a blessing that Tim was not part of those experiments otherwise we 'd be still living w/o dEs ;) or may be we 'd have a better system - who knows
-
The mystery continues, just got a reference tested lamp from my dealer. Unfortunately it was a 50W lamp and my DC power supply can only get it up to 12.4 volts then (I bought 35W lamps), and it became 3700K at that voltage.
Getting paranoid, I made visual comparison with a Grafilite Mode A3 fluorescent which others than me has measured to ~5500-5600K (I get the same result), and clearly the light from that is bluer.
I also did the white balance picker thing, with high CRI sources color temp can be guess quite well by the camera and indeed it shows almost exactly the same values as I measure (a little varmer as the paper is not 100% white).
The other picture attached with the brighter lamp is the 35W run at 16.4 volts, and then I get 4700-4800K, but voltage is way too high for that.
It doesn't seem likely that the measurements are wrong, considering both methods showing the same thing, and other lamp measurements matching other people results.
So I need to try with a different power source and see if I get some other result, there still could be some issue with my DC power supply. I have measured it, but only the voltage, maybe it does something funky when delivering power...
-
there still could be some issue with my DC power supply
Don't Solux bulbs normally run on 12 volts AC? I don't have an official Solux fixture. What I did was get a 60 watt 120 volt (USA) to 12 volt transformer that was in the outdoor lighting section of my local hardware store. And a MR-16 fixture that was designed for outdoor lighting. I wired everything together and taped it to a mike stand.
I have an AC variac (transformer with a movable tap, so the output can be varied from below normal voltage to above normal voltage. Was used for troubleshooting electronics--to see if the device only flaked out on high or low line voltage.) I was going to disassemble my fixture so I could get to the wires, plug it into the variac, and use my multimeter to monitor the voltage on the light fixture (after the 12 volt transformer). I haven't done this yet. (My multimeter is old and was acting flaky. I wanted to get a new multimeter.)
With AC, it is tricky. There is peak voltage, peak-to-peak voltage, and RMS. I'm not sure which corresponds to DC voltage. And I'm not sure which my meter measures. (I was going to plug the fixture in without the variac and see what it measured on the lamp terminals.)
Does running on DC instead of AC make any difference?
Wayne
-
With AC, it is tricky. There is peak voltage, peak-to-peak voltage, and RMS. I'm not sure which corresponds to DC voltage.
For power, you need RMS, but it isn't difficult to convert if you know that it is a sine wave, and that's what is typically assumed with simpler meters.
It's much more difficult to measure true RMS when the waveform is not a sine wave - you need either a tricky thermal system, or some clever electronics or digital sampling and maths.
-
Halogen lamps should work on both AC and DC. I always thought the the typical was DC and the Solux voltage numbers were for that, but it's surely worth investigating... electricity is not my best area of knowledge so I don't really know what differences to expect.
In this report they talk about a DC power supply though, so I think it should work. May be my power supply that is simply bad.
http://www.babelcolor.com/download/Light_under_control_2005-11-08.pdf
-
Halogen lamps should work on both AC and DC. I always thought the the typical was DC and the Solux voltage numbers were for that, but it's surely worth investigating... electricity is not my best area of knowledge so I don't really know what differences to expect.
In this report they talk about a DC power supply though, so I think it should work. May be my power supply that is simply bad.
http://www.babelcolor.com/download/Light_under_control_2005-11-08.pdf
typical halogen power supply delier 11.5volt on its terminals. Add to that the voltage drop over the cable a d you easily get close to 11 volts. You can check on the solux datasheet the drop in kelvin.
-
Got some better measurement gear. The power supply meter does seem to show the correct result. The culprit are seems to be the lab cables I got with the power supply that is bad, I lose 5 volts(!) over them, leaving the lamp under-powered. I haven't yet been able to get proper cables, but it does indicate as soon as I get them the lamps will be on spec, like they've always been.
So it seems to be one of those user errors after all, I guess they need to add one more item to their list of user mistakes...
I'll report back when I've got to test with better quality cables. I think DC instead of AC should be okay, and hopefully it is because it's a lot easier (and cheaper) to get variable DC power supply than a variable AC power supply in a suitable range, at least around here.
-
Did a quick test without having proper cables, but making an ugly-connect of the socket directly, and then the lamp holds the promise. The 45watt power supply I got get problems overdriving the 35watt lamp though, due to that it requires more than 3 amperes. I get it up to 12.4 volts though which makes one of my lamps just reach 5000K CCT which is all I need.
Actually reading on the description of the lab cables that says "max 2 amps", and actually divding 35watt / 11.5volts = 3.04 amps had been a good thing to do. Than I'd known that the cables were not adequate and the power supply (indeed 45 watts, but max 3 amps) a bit too weak. Duh...
Although it seems like my current supply makes it with the smallest possible margin, I may sell this and get a proper one just to punish myself :-).
-
Bewaren that when still cold the lamp draws a lot more ampère. Regulated power supplies need to be oversized by factor of 3 to delier the startup current.
-
Or use what we in the US call a "ballast"
-
In this case we want the light warm and stable, so delivering extra current early on should not be needed, right? Or are you referring to short circuit protection?
Anyway, bought a bigger power source now and some decent cables, going to test after work today.
-
So at last, with a proper power source, got a 0-30V 0-5A DC lab variable power supply, and proper cabling I got it to work as promised. All my fault, no shadow on Solux.
With one of my Solux 4700K 35W lamps I got 5000K CCT at 13.2volts, 3.25 ampere, and 5500K at 15.8volts 3.6 ampere.
Both the D50 and D55 simulation looks fine, although running it at 15.8 volts is really pushing it of course. For some quick camera profiling shots should be okay.
I've attached another alternative to simulate daylight, using a standard 3000K halogen spotlight and put a film photography 80B light balancing cooling filter in front. Note that the scale reaches 1.4 to fit the bump making it look a little flatter than it should compared to the others. My conclusion is that this filter method does not work well enough, using a Solux is better.
-
In this case we want the light warm and stable, so delivering extra current early on should not be needed, right? Or are you referring to short circuit protection?
Anyway, bought a bigger power source now and some decent cables, going to test after work today.
If cables got warm, the resistance goes up. Cables need to be 3x-5x current rated.
-
I'm using 10A cables now, seems to work fine, the old one were only 2A designed for measurement...
-
I'm using 10A cables now, seems to work fine, the old one were only 2A designed for measurement...
so you hook the cables directly to the bulb contacts then ?
-
I'm using 10A cables now, seems to work fine, the old one were only 2A designed for measurement...
Yes, 10A cables is quite a guarantee. Especially if they are copper.
-
Yes, 10A cables is quite a guarantee. Especially if they are copper.
The rating of a cable depends on the parameter used to determine it. Typically this will be a temperature limit - i.e. what current can you pass through the cable before it gets so hot that the insulation is in danger of melting ?
For the purposes of this particular exercise, the important parameter is the voltage drop though the cables, which translates to the required maximum cable resistance.
-
The rating of a cable depends on the parameter used to determine it. Typically this will be a temperature limit - i.e. what current can you pass through the cable before it gets so hot that the insulation is in danger of melting ?
For the purposes of this particular exercise, the important parameter is the voltage drop though the cables, which translates to the required maximum cable resistance.
There are many factors, including cable length, that affect voltage drop. The rule of thumb is to have 3x to 5x Amps rating against what a generic brand manufacturer states on a cord (that is, if it is stated 10 Amps, one can expect 2-3 Amps without a serious voltage drop), and that is for reasonably short cables. 10 Amps power transmission is a copper wire of approx. 1mm diameter (18 AWG); but in household (short cords) they can use 0.4mm - which, in turn, is rated for 0.36 Amps only for power transmission. One can use a calculator like http://www.rapidtables.com/calc/wire/voltage-drop-calculator.htm